Taken together, theory-guided nano-engineering of organic electro-optic materials and hybrid device architectures have permitted dramatic improvement of the performance of electro-optic devices. For example, the voltage-length product has been improved by nearly a factor of 104 , bandwidths have been extended to nearly 200 GHz, device footprints reduced to less than 200 μm2 , and femtojoule energy efficiency achieved. This presentation discusses the utilization of new coarse-grained theoretical methods and advanced quantum mechanical methods to quantitatively simulate the physical properties of new classes of organic electro-optic materials and to evaluate their performance in nanoscopic device architectures, accounting for the effect on chromophore ordering at interfaces in nanoscopic waveguides.

Short wavelength infrared (SWIR) sensors are important to applications in environmental monitoring, medical diagnosis and optical communications, but there are only a few organic semiconductors that show optoelectronic response in the SWIR region. Recently we demonstrated a family of novel donor-acceptor polymers with narrow bandgap responsive in the SWIR region, and the bulk heterojunction photodiodes based on these polymers show detectivity up to 1E11 Jones at a wavelength of 1.37 micron, with absorption edge extending out to 1.7 micron. A SWIR photodiode was incorporated into the etalon-array reconstructive spectroscopy system to demonstrate its imaging capabilities.
As the initial performance is very promising, we proceed to investigate the stability of the encapsulated devices and to infer the degradation mechanisms. The performance of photodiodes were monitored by IV measurement, external quantum efficiency (EQE) and electrochemical impedance spectroscopy. The IV measurement and electrochemical impedance spectroscopy were conducted both in the dark and under illumination, to track over several weeks the change in charge generation and recombination processes under the short circuit and open circuit conditions. The characteristics from band-to-band absorption and from absorption in charge-transfer states were compared to quantify the lifetime and recombination losses of photogenerated carriers in these devices.

Organic photodetectors (OPDs) are attracting interest as various sensing platforms such as photo/chemical sensors, healthcare sensors, x-ray scanner, and image sensors. In particular, a distinct advantage of organic materials, i.e., orthogonal photosensitivity to the specific wavelength such as blue (B), green (G), red (R), and even infrared has recently facilitated promising applications to organic full colour image sensors. For instance, vertical stacks of G-wavelength selective organic photoconversion layers on conventional Si CMOS imagers with B/R color filters have been made to realize highly sensitive image sensors by doubling the light detecting area compared to the planar R/G/B pixel structure.
Our recent investigations on small molecule OPDs with bulk heterojunction structure have shown high peak external quantum efficiencies over 60% and extremely low dark current densities below 0.1 nA/cm2 at reverse bias of 3V, which are comparable to the typical performance of Si-based PDs. On the other hand, their photoresponse characteristics have not been systematically studied. For example, the Si PD exhibited the rising time of photoresponse speed as fast as 10 us at 99.9% of the peak photocurrent, whereas the OPD showed 20 times slower response time plausibly due to the reduced charge carrier mobility. Thus, in order to investigate the practical use of OPDs as image sensor applications, we will present the current status of dynamic characteristics of OPDs in terms of photoresponse speed, frequency response, and transient photocurrent. Further, the possible origin of photoresponse characteristics of OPDs will be described.

There is a big need for electronic biosensors that can be operated in water for biomedical applications and environmental monitoring. Devices based on organic materials are currently attracting great attention for applications where low-cost, large area coverage and flexibility are required. Water is an aggressive medium and due to its chemical activity the operational voltage window for stable sensor operation is limited. Related to that, in the past, degradation under both ambient and aqueous environments have limited their application in bio sensors for portable, label-free detection in the field of healthcare and environmental monitoring.
Quite recently, our group has demonstrated stable FET device operation based on organic active materials directly exposed to water and more interestingly, even sea water.[1-3] By pattering an array of gold nano-particles on top of the organic semiconductor but close to the transistor channel, the developed structure was able to sense low concentrations of mercury ions in sea water.[2,3]
Here we would like to present the second generation of this highly sensitive bio-sensor platform based on organic field-effect transistors developed in our group able to operate at even lower voltages which is a necessary condition for stable device operation in water based environments.[4,5] Functionalization is a powerful tool to attach receptor units close to the transistor channel which are able to detect its corresponding analytes. This methodology allows preparing a scalable, easy producible and high performing sensor platform suitable for portable biosensing in aqueous media.
[1] M. E. Roberts et. al., PNAS, 105, 12134 –12139, 2008.
[2] M. L. Hammock et al., ACSNano, 6, 3100-3108, 2012.
[3] O. Knopfmacher et. al. Nature Communications, 5, 2954, 2014.
[4] C. Wang, et al. Scientific Reports, 5, 17849, 2015.
[5] D. Kong, et al. Advanced Functional Materials, 26, 4680–4686, 2016.

We report on a fluorescent optoelectronic nose for the trace detection of nitroaromatic explosive vapors. The sensor arrays, fabricated by aerosol-jet printing, consist of six different polymers as transducers. We demonstrate the nose’s ability to discriminate between several nitroaromatics including nitrobenzene, 1,3-dinitrobenzene and 2,4-dinitrotoluene at three different concentrations using linear discriminant analysis (LDA). We assess the within-batch reproducibility of the printing process and we report that the sensor polymers show efficient fluorescence quenching capabilities with detection limits of a few parts-per-billion in air.
Our approach enables the realization of highly integrated optical sensor arrays in optoelectronic noses for the sensitive and selective detection of nitroaromatic explosive trace vapors using a potentially low-cost digital printing technique suitable for high-volume fabrication. An important challenge is temperature-dependence which is often neglected even though organic emitters are strongly affected by temperature. For some materials, even small changes of a few Kelvin can lead to large changes in the emission intensity making a temperature-control for sensing applications inevitable. Therefore, the temperature-dependence of these sensors is investigated via a heated transparent thin film on the back of such sensors allowing the active layer to be temperature controlled. All of these led to the development of a portable system.

Recent development of 3D printing technologies would provide the variety of electronic devices including environmental sensors and bio-applications. Polymer-based sensors are compatible with human-body parts or prostheses to monitor the body status of surfaces or surroundings such as temperature, humidity, and pressure. Conventional 1D or 2D fabrication processes are effective for mass production. However, specific shapes such as curvy or 3D pathways would require the 3D printed sensors to expand the possible applications.
In this study, organic temperature sensors fabricated on 3D printed surfaces are investigated to improve the device properties. 3D structures were fabricated using a DLP (direct light processing) 3D printer with photo-polymers. Sensor electrodes based on conductive carbon materials were printed on 3D shape structures. The resistances of organic temperature sensors were measured by the temperature variations. As the environmental temperature increased from 29 to 54℃, the resistance was decreased from 8.57 to 8.23 kΩ with the certain linearity, respectively. To further improvements, polymer composites comprising the inorganic nanoparticles were introduced to control the interfacial properties and the conductivity of composite carbons were improved.

Tattoo-like epidermal sensors are an emerging class of truly wearable electronics owing to their thinness and softness. While most of them are based on thin metal films, silicon membrane, or nanoparticle-based printable inks, we report the first demonstration of sub-micron thick, multimodal electronic tattoo sensors that are made of graphene. The graphene electronic tattoo (GET) is designed with filamentary serpentines and fabricated by a cost- and time-effective “wet transfer, dry patterning” method. It has a total thickness of 463 ± 30 nm, an optical transparency of ~85%, and a stretchability of more than 40%. GET can be directly laminated on human skin just like a temporary tattoo and can fully conform to the microscopic morphology of the surface of skin via just van der Waals forces. The open mesh structure of GET makes it breathable and its stiffness negligible. Bare GET is able to stay attached to skin, for several hours, without fracture or delamination. With liquid bandage coverage, GET may stay functional on skin up to several days. As a dry electrode, GET-skin interface impedance is on par with medically used silver/silver-chloride (Ag/AgCl) gel electrodes, while offering superior comfort, mobility and reliability. GET has been successfully applied to measure electrocardiogram (ECG), electromyogram (EMG), electroencephalogram (EEG), skin temperature, and skin hydration. Graphene represents a new facile route for ultra-conformable multifunctional electronic tattoos, and paves the path for the introduction of other two dimensional materials for future advanced tattoo systems.

Biodetection using electrolyte gated field effect transistors has been mainly correlated to charge modulated transduction. Therefore, such platforms are designed and studied for limited applications involving relatively small charged species and much care is taken in the operating conditions particularly pH and salt concentration (ionic strength). However, there are several reports suggesting that the device conductance can also be very sensitive towards variations in the capacitance coupling. Understanding the sensing mechanism is important for further exploitation of these promising sensors in broader range of applications. In this paper, we present a thorough and in depth study of a multilayer protein system coupled to an electrolyte gated transistor. It is demonstrated that detection associated to a binding event taking place at a distance of 30 nm far from the organic semiconductor-electrolyte interface is possible and the device conductance is dominated by Donnan’s capacitance of anchored biomolecules.

Charge Modulated OTFTs represent a versatile tool for the realization of a wide range of sensing applications. The architecture is based on a floating gate organic transistor whose sensitivity to a specific target is obtained by properly functionalizing a part of the floating gate with a sensing layer that can be chosen according to the specific external stimulus to be sensed.
In this work we will show that such devices can be routinely fabricated on highly flexible, ultra-conformable thin films and that they can be employed, with no need of any chemical modification of the sensing area, for monitoring pH variations featuring a super-nernstian sensitivity. Interestingly, we will also show that the proposed approach has been applied for monitoring cell metabolic activity, demonstrated with a preliminary validation. In addition this device can be used for monitoring electrical activity of excitable cells, thus giving rise to a new family of highly sensitive, reference-less, and low-cost devices for a wide range of bio-sensing applications.
Finally, we will also demonstrate that using a different sensing layer it is possible to employ the same device architecture for the realization of matrices of multimodal tactile transducers capable to detect at the same time temperature and pressure stimuli, and that being fabricated on sub-micrometer thin film can be conformably transferred on whatever kind of surface allowing the reproduction of the sense of touch.

The rapid detection of disease specific biomarkers in a clinically relevant range using a low-cost sensor can facilitate the development of individual treatment plans for a given patient, known as precision, personalized or genomic medicine. In the recent decade Electrolyte-Gated Organic Field Effect Transistors (EGOFETs), a subtype of OFETs where the dielectric is replaced by an electrolyte, have attracted a great deal of attention for sensing applications. This is due to their capacity to operate at low voltage (< 1 volt) in physiological like media. Although EGOFET based biosensors have been shown to specifically detect biomolecules with high sensitivity and selectivity; the stability, reproducibility, and performance required to reach the desired market are not yet achieved. In this contribution, we describe the development of a stable and reproducible EGOFET sensor that is able to detect biomolecules selectively in real-time. Facile and scalable techniques are used to prepare arrays of these devices. The selectivity of individual EGOFETs is investigated by immobilization of specific ligands to the target molecule of interest on the gate electrode within a microfluidic flow cell.

We present the construction and the application of biocompatible micro- and nano-structures that can be administered systemically and transport in a targeted and effective way drugs, small molecules, stem cells or immune system cells. These polymeric nano-systems represent a primary goal for the treatment of a wide family of neurological/systemic disorders, as well as tumors and/or acute injuries. As natural, biocompatible, biodegradable and non-immunogenic building blocks, alginate and chitosan are been currently exploited. Ionotropic pre-gelation of the alginate core, followed by chitosan polyelectrolyte complexation, allows to encapsulate selected active molecules by means of physical entrapment and electrostatic interactions within sub-micron sized hydrogel vesicles. Here we present a microfluidicassisted assembly method of nano- and micro-vesicles -under sterile, closed environment and gas exchange adjustable conditions, which is a critical issue, when the cargo to be uploaded is very sensitive. Polymer/polymer and polymer/drug mass ratio relationship are crucial in order to attain the optimum in terms of shuttle size and cargo concentration. By modulating polymer reticulation conditions, it become possible to control drug loading efficiency as well as drug delivery dynamics. Recent results on the application of these vesicles for the encapsulation and delivery of Inhibin-A and Decorin, proteins involved in acute kidney injury (AKI), for Renal tubular cell regeneration will be presented. Finally, the impact of these polysaccharide sub-micron vesicles on Human Immune cells and the metabolic and functional activity of cells embedded in the assembled vesicles will be presented and discussed.

Direct integration of an infrared-sensing quantum dot film and an organic light-emitting diode (OLED) offers pixel-free infrared imaging. However, the infrared-to-visible conversion efficiencies of the devices are low due to the low photon-to-electron conversion efficiency of the quantum dot photodetector. Here, we report a novel vertical infrared phototransistor with 105 % external quantum efficiency (EQE). By integrating a phosphorescent OLED with this phototransistor, an infrared-to-visible up-conversion light-emitting phototransistor with an EQE over 1,000% is demonstrated. In addition, by employing a ferroelectric gate insulator for the vertical transistor, a flexible low voltage non-volatile memory is demonstrated with 10 years of retention extrapolated.

Progress in bionic sensing and bio-electronic interfacing requires a thorough understanding of electronic and ionic transport in functional bio-compatible materials. The well-known polymer mixture poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is central to many optoelectronic applications which necessitate flexible, transparent biocompatible materials. While PEDOT:PSS is traditionally studied for its hole transport properties and resistive H2O response, research interest has recently turned to ionic transport in the context of bio-electronic interfacing and sensing. Cations Na+ and K+ are often present in PEDOT:PSS as byproducts from industrial production. Uptake of water into PEDOT:PSS disrupts hydrogen bonding that maintains rigidity of the PSS matrix, causing film swelling and hydronium production due to water interaction at the hydrophilic SO3- moiety. As water uptake increases, mobility of Na+, K+, H3O+ and other ions may become hindered due to the formation of electrical double layers and hydration shells around ions. At the same time, water-induced swelling of the PSS matrix increases the distance between adjacent conductive PEDOT domains, which reduces electronic mobility. Despite its widespread use as a hole transport material in a variety of organic optoelectronic devices, the effect of water on electronic and ionic transport in PEDOT:PSS remains unclear. To probe both electronic and ionic response during water uptake, we perform ultra-wide range dielectric spectroscopy from sub-Hz to optical frequencies while changing humidity conditions in a controlled environment. We correlate the frequency-dependent measurements with those of a PEDOT:PSS-coated quartz crystal microbalance (QCM) to estimate the mass of adsorbed H2O in the film. We show that the presence of water has an effect on electronic and ionic mobility in the film and both electronic and ionic transport play a role in defining the optoelectornic properties of PEDOT:PSS under a wide range of humidities.

Direct measurement and stimulation of electrophysiological activity is a staple of neural and cardiac health monitoring, diagnosis and/or therapy. Such bi-directional interfacing can be enhanced by the low impedance imparted by organic electronic materials that show mixed conduction properties (both electronic and ionic transport). Many high performance bioelectronic devices are based on conducting polymers such as poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS. By investigating PEDOT-based materials and devices, we are able to establish a set of design rules for new formulations/materials. Introducing glycolated side chains to carefully selected semiconducting polymer backbones, for example, has enabled a new class of high performance bioelectronic materials that feature high volumetric capacitance, transconductance >10mS (device dimensions ca. 10um), and steep subthreshold switching characteristics. A sub-set of these materials outperform PEDOT:PSS and shows significant promise for biocompatible, low power in vitro and in vivo biosensing applications.

A rapid and low cost photoluminescence (PL) immunosensor for the determination of low concentrations of Ochratoxin A(OTA) and Aflatoxine B1 (AfB1) has been developed. This biosensor was based on porous silicon (PSi) fabricated by metal-assisted chemical etching (MACE) and modified by antibodies against OTA/AfB1 (anti-OTA/anti-AfB1). Biofunctionalization method of the PSi surface by anti-OTA/ anti-AfB1 was developed. The changes of the PL intensity after interaction of the immobilized anti-OTA/anti-AfB1with OTA/AfB1 antigens were used as biosensor signal, allowing sensitive and selective detection of OTA/AfB1 antigens in BSA solution. The sensitivity of the reported optical biosensor towards OTA/AfB1 antigens is in the range from 10-3 to 102 ng/ml.

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Journal of Applied Remote SensingJournal of Astronomical Telescopes Instruments and SystemsJournal of Biomedical OpticsJournal of Electronic ImagingJournal of Medical ImagingJournal of Micro/Nanolithography, MEMS, and MOEMSJournal of NanophotonicsJournal of Photonics for EnergyNeurophotonicsOptical EngineeringSPIE Reviews